The present invention relates to an electrophotographic recording, and more particularly to an apparatus and method for selectively controlling the amount of light exposed onto a photosensitive drum without being controlled by a developing unit when the apparatus prints printing information.
Generally, the art of printing using an electrophotographic developing technique is well known as xerography. The apparatus whether a laser beam printer, facsimile or photocopier, as its basic principle, utilizes an adhesive force of static electricity and an optically conductive semi-conductor with differences in electricity conducting rates controlled according to exposure to the light. Among these printers, the laser beam printer is a printing device that uses a laser diode as its light source instead of a special fluorescent lamp or a mercury lamp, and prints the printing data provided as, for example, video data for a source such as a computer, etc., on a printable medium such as individual sheets of printing paper, instead of merely reproducing images reflected from a document. As described above, recently developed laser printers, in comparison with the conventional impact printers that print letters by using hammers striking a platen, have a higher printing speed, lower noise level, and form finer shapes of printed letters. Also, they are very popular and widely used because they are easily linked with computers to receive signals conveying information to be printed such as a text signal of a video signal.
The printing process of such laser beam printers includes a developing stage where a toner used as a developing material is attracted to a latent image formed on the photosensitive drum by exposure of the photosensitive drum to light, a transferring stage where the toner attracted to the drum is transferred to a printable medium such as a sheet of paper fed by a feed roller, and a fusing stage where the toner that had been transferred onto the printable medium is fused is then fused onto the printable medium. These stages of the process also are generally known in the current art.
In the printing process mentioned above, it is the developing stage that is closely related to a consumption of the toner, and that directly affects the printing quality. Moreover, in order for a conventional printer to control the printing density, the bias voltage of a developer is changed to adjust the amount of the toner developed. See, by way of further explanation, the IMAGE FORMING APPARATUS COMPRISING MEANS FOR SETTING A PROPER BIAS VOLTAGE OF LASER EMITTING MEANS AND METHOD THEREFORE by S. Ogino, et al, U.S. Pat. No. 5,061,949. In one contemporary approach to control printing density, a print control unit controls printing of video data with electrical signals and supplies beam data, used during scanning of an image onto the circumstantial exterior surface of the drum with a beam of light emitted by the light source element video data signal. This may be seen in for example, the PICTURE REPRODUCING APPARATUS of M. Yamamoto, et al., U.S. Pat. No. 3,894,182. Also, the print control unit receives beam detection signals generated by the light source element and supplies a horizontal synchronization signal and a bias voltage control signal to a bias voltage generator that provides the bias voltage to the developer.
The amount of toner attached on the drum during the developing stage is determined by the bias voltage and the intensity of the bias voltage is controlled by an adjusting terminal known as a printing density selecting switch, installed on the control panel in an external stage of the printer. A printer using this approach to control of printing density is very inconvenient to use however, because the printing density has to be adjusted for each use. Moreover, this approach requires intense, uninterrupted concentration from the user. Also, it is very hard for unskilled users to accurately and repeatedly adjust the adjustment terminal. Frequently, the durability of the photosensitive drum in such laser printer is shortened and the toner consumption is increased when the user fails to adjust the bias voltage properly.
Accordingly, it is an object of the present invention to provide an improved printing process and apparatus.
It is another object to provide a method and apparatus for selectively controlling the amount of light illuminating the photosensitive drum without controlling the developing unit when an image is printed with a laser beam being used as a light signal.
It is a further object to provide a laser reproduction process and printer offering an optimum printing quality by automatically, internally selecting the amount of light illuminating the photosensitive drum.
It is a still further object to provide a laser printing process and printer having a simple circuit externally adjusting the sharpness of characters, symbols, and graphs to be printed during the process.
It is a yet further object to provide a process and control circuit for reliably controlling toner consumption in an electrophotographic developer.
It is a still yet further object to enable a user of an electrophotographic developer type printer to transmit to a printer data controlling print quality while transmitting data defining the images to be printed by the printer.
These and other objects mentioned above, may be achieved according to the principles of the present invention with a process and an apparatus using a data transmitting unit converting video data in response to a horizontal synchronization signal applied with a predetermined time interval by converting data to be printed into a series of lines of serial video data in accordance with a first clock signal, and a printing control unit regulating a mechanism used to print the video data by generating electrical signals representing the video data, providing beam data used to switch the generation of light provided by a light source element that had been obtained from chopped video data applied to the light source element, and generating a horizontal synchronization signal by processing a beam detection signal produced by the light source element. A chopping unit connected between the data transmitting unit and the printing control unit chops the converted video data received from the data transmitting unit in response to a second clock signal, and provides the chopped video data.
According to the present invention, printing may be performed by converting data to be printed into a series of lines of video data in accordance with a first clock signal and transmitting the converted video data in response to a horizontal synchronization signal exhibiting a predetermined time interval. Chopped video data is generated by chopping the converted video data in response to a second clock signal; and beam data obtained from the chopped video data is supplied for controlling the light generation of a light source element. The horizontal synchronization signal is operated by processing a beam detection signal resulting from the beam of light produced by the light source element.
In the practice of the present invention, the frequency of the first clock signal is set to be either equal to or lower than the frequency of the second clock signal. If the frequency ratio between the first and second clock signals is an integer multiple, a single divider stage may be used; the first and second clock signals should then be generated from different output terminals of the divider stage.
According to the configuration and method of the present invention, the chopped video data is generated by the printing control unit as beam data, and is then used for controlling the amount of light illuminating the photosensitive drum. The amount of the light is optimally controlled by selecting the second clock signal. Therefore, the user can adjust the density of printed images by designating or selecting the data defining the amount of light exposed by means of software. By doing so, the sharpness of the printed images can be easily adjusted without adjusting the bias voltage of a developing unit.